Yeah, I pre-grind about a week or two's worth. Light, air and heat is what degrades the bud. Take care of those situations, and your bud will last a pretty long time. Pre-grinding causes your bud to dry out a bit faster, but again, in the time frame the OP is talking about, it really won't make much of a difference, if any.

A day's worth is definitely A-OK.
Hell, even a week or so is hard to notice any quality differences to me at least.

Per advice found in this forum, I keep three strains on me -- one mid strain that I pre-grind and let sit for weeks if needed (use with highest frequency), one higher quality strain that I freshly grind (use a bit less), and a top shelf that I also only freshly grind (only on special occasions).

The three strain method staves off tolerance. Not really sure why. Just read it on this forum, and it definitely feels like it works.

I used to vape exactly theses amounts Vicky, for like two years. But once you've slipped to more (avg .53 per day for me) its really tough to slow down.
I don't pre grind exactly, I pre load my two bowls, but having directly available ground up stuff tends to make me use even more. That's how I ended upping my tolerance not noticing what amounts I was using. But if I had more supply I definitely would always have some ground up stuff.